1. Field of the Invention
The present invention relates to a brake-equipped retracting mechanism whereby a retractable member such as a liquid crystal display device installed in the ceiling of a passenger cabin of an aircraft or the like is swung between a retracted position and an open position.
2. Description of the Related Art
Liquid crystal display devices are installed in ceilings of passenger cabins in aircrafts or the like, and these devices are retracted horizontally in the ceiling and are opened to a substantially vertical open position when necessary. When the liquid crystal display device opens, rotational motion outputted via a motor and a reducer is converted to pivoting movement for opening the liquid crystal display device to the open position via a link mechanism. A power spring is linked to an input or output shaft of the reducer, and the power spring is designed to be wound up in conjunction with the opening movement of the liquid crystal display device. When the liquid crystal display device is retracted, the motor and reducer are disconnected by an electromagnetic clutch, and the liquid crystal display device is returned to the retracted position by restoring force of the wound-up power spring. The reason that the retracting operation should not be dependent on rotational force of the motor is because of a requirement for the liquid crystal display device to be reliably returned to a safe retracted position without relying on an electric force during emergencies.
As shown in FIG. 5(b), a liquid crystal display device 1 is substantially horizontal position in a retracted position 1A, and is substantially vertical position in an open position 1B. Therefore, as shown in FIG. 5(a), a torque T(1) that is generated by the own weight of the liquid crystal display device 1 and urges the device to pivot in an opening direction is greatest in the retracted position, decreases as the device pivots to the open position 1B, and reaches a minimum at the vertical position. By contrast, restoring force T(18) of the power spring is lowest when the liquid crystal display device 1 is retracted because the power spring is wound the lowest number of times (initial winding state), and the restoring force T(18) is at a maximum when the liquid crystal display device 1 reaches the open position 1B, because the number of windings is at a maximum. In order to return the liquid crystal display device 1 to the retracted position 1A with the aid of the power spring, the restoring force T(18) in the initial winding state must exceed the torque T(1) in the opening direction due to the own weight of the liquid crystal display device 1 in the retracted position.
If restoring force of the power spring is set in this manner, the torque reaches a maximum in the open position and a return torque T(1+18) is applied, which decreases toward the retracted position. The return torque in the open position is extremely strong, which is dangerous because it causes an abrupt closure of the liquid crystal display device 1. In view of this, a retracting mechanism of the liquid crystal display device 1 is provided with a brake mechanism for applying a brake so that the liquid crystal display device closes at an appropriate speed. Conventionally, a gear damper, which increases braking force in proportion to the speed, is used.
However, the gear damper is configured so that multiple gears are provided and frictional force is enhanced by centrifugal force, which leads to problems with complicated mechanisms and poor reliability.